The following subclasses and interfaces have been renamed accordingly.Drupal\Core\Entity\Field\Field-->\Drupal\Core\Field\FieldItemListDrupal\Core\Entity\Field\FieldInterface-->\Drupal\Core\Field\FieldItemListInterface\Drupal\file\Plugin\field\field_type\FileField-->\Drupal\file\Plugin\Field\FieldType\FileFieldItemList